Pipeline Inspection Tools

The corrosivity of fluids being transported along sub-sea or buried onshore pipelines can be assessed using standard monitoring techniqnes at accessible locations, which are usually limited to each end of the pipeline. However, detection of localized corrosion of the pipe wall reqnires the use of inteUi-gent pigs. 

There are two principle types of inspection vehicle used to survey the internal and/or external condition of steel transmission pipelines. The first involves the direct measurement of wall thickness by ultrasonics. The second uses an induced magnetic flux in the pipe wall to assess the defect size from the perturbation caused by defects. Both techniques require the pipe internals to be thoronghly cleaned and free of deposits for them to function successfiiUy. 

Ultrasonic pigs have the advantage that they measure wall thickness directly. There is also no practical limit to the pipe wall thickness that can be measured and the results are not affected by the proximity of girth welds. 

They have the disadvantage that, as with aU ultrasonic measurements, a conplant is reqnired between the sensing head and the pipe wall. This means that for successful use in gas lines nltrasonic pigs require to be run in slugs of a couplant such as methanol or glycol, or behind a gel pig. 

In older pipelines, where significant internal wastage has occurred, the rehabUity of ultrasonic pigs is questionable due to the reduced intensity of the reflected signal from the non-planar snrface. 

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Pipeline inspection tools depend on the type of pipe and the level of details which the owner chooses to budget for during the inspection. One of the most cost-effective... 

Figure 12.19 Magnetic flux leakage ILI tool designed for high-speed gas pipeline applications. (Courtesy of BJ Pipeline Inspection Services)...

Electromagnetic acoustic tools are particularly adapted to the detection of cracks in dry gas pipelines. This tool generates ultrasonic signals without requiring liquid couplant to transfer the ultrasound into the steel. These tools are new to the pipeline inspection industry, so their effectiveness has not yet been determined. 

A pipeline inspection gauge, or pig , is a tool with which, among many other tasks and benefits, pipelines are cleaned and/or inspected internally. Figure 9.1a shows an example of a pig to be used for cleaning natural gas pipelines. Figure 9. lb illustrates the relative size of a pig. 

Another tool the interstates use to maintain their pipelines is a device known as an intelligent pig. Propelled through the pipeline with the gas stream, these devices, taking thousands of measurements with electronic sensors that can be analyzed later by computers, can inspect pipeline interior walls for corrosion or other defects and remove accumulated debris from a section of pipeline. Pipelines also use state-of-the-art coating and cathodic protection to battle corrosion. 

In-line inspections (ILI) are useful in obtaining a profile of defects in a pipeline. High-resolution UT and MFL ILI tools can be used to determine the geometry and orientation of corrosion defects. 

As a result of regulatoiy changes in the U.S., the pipeline industry needed an alternative method to pressure testing on in-line tool inspection to assess buried pipelines [33], EDCA is a four-step process consisting of ... 

Only fully inspected and properly maintained equipment should be allowed on site. This applies to power shovels, concrete mixers, supply trucks, cranes, materials handling devices, power tools, and other construction equipment. Great care must be taken to avoid collisions of mobile equipment with production equipment, pipelines, power lines, staged materials, or other objects or hazards. Specific measures include the use of permit programs, warning signs, personnel training, site reviews, and careful supervision. 

A separate incident on an Olympic pipeline led, on September 17, 1996, to the Washington Department of Ecology ordering Olympic to carry out further remote inspection work, including the use of a diverse (mechanical) measurement technique called caliper tools . This led, on January 15, 1997, to another inspection of the pipeline done by a different company, Enduro, using the caliper tool inspection... 

In-line inspection (ILI) tools, also commonly called "smart" or "intelligent pigs," are cylinder-shaped electronic devices used by the pipeline industry to detect loss of metal and in some cases deformations... 

However, most internal repair methods are used for low operating pressure pipelines and only to restore leak tightness (Toutanji and Dempsey, 2001). Also, these internal repair systems are considered to cause reductions in the inside diameter of pipelines that may hinder the ability to clean and inspect them using traditional tools. Thus, the use of composite materials for internal repair of pipes presents a number of difficulties that have yet to be fully explored. 

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